Ultraviolet-B effects on Spirodela oligorrhiza: Induction of different protection mechanisms

Ultraviolet-B (UV-B) tolerance in plants has mostly been correlated with the presence of screening pigments (e.g. flavonoids) or other reductions in leaf transmittance. We have exploited the rapid turnover of the Photosystem II reaction center protein D1 as a sensitive in vivo probe for UV-B damage. We found that the aquatic monocot, Spirodela oligorrhiza, protects itself from UV-B irradiance using at least three different mechanisms. In one case, protection is correlated to the presence of UV-B screening pigments; in the second, an elevated oxygen-radical detoxifying system parallels UV-B tolerance; while in a third, UV-B tolerance is related to a mechanism involving neither screening pigments nor increased radical scavenging capacity. This demonstrates that, in vivo, a plant can complement its UV-screening and attenuation strategies by other tactics as well.